1. Field of the Invention
The present invention relates to switch devices for operating electric power tools, such as hand-held disk grinders for stone cutting use and others.
2. Description of the Related Art
A known hand-held disk grinder includes a body part, a gear head, and a handle. The body part is provided therein an electric motor serving as a driving source. The gear head is mounted to the front portion of the body part, and the handle is mounted to the rear portion of the body part.
The gear head includes a gear case, in which a gear train is provided for reducing the rotation of the electric motor. The rotation after reduction by the gear train is transmitted to a spindle, to which a disk-shaped grindstone is mounted.
The handle can be held by a user of the electric power tool with his or her hand, and the lower portion thereof is provided with a switch lever that can be pulled or slid by the user between an ON position and an OFF position using his or her finger tip. When the user moves the switch lever to the ON position by pulling it using his or her finger tip while holding the handle (i.e., grasping the switch lever together with the handle), a power supply circuit is turned ON so that the electric motor in the body part is started. In response to starting of the electric motor, the rotation thereof is transmitted to the spindle via a driving head so that the grindstone is rotated. When the switch lever is released from being pulled, the switch lever is responsively returned to the OFF position by a spring biasing force or others, and the power supply circuit is thus cut off, whereby the electric motor is stopped.
As such switch devices having switch levers, those provided with on-lock and off-lock mechanisms have been proposed. With the on-lock mechanism, the switch lever is locked in the ON position, and with the off-lock mechanism, the switch lever is locked in the OFF position. With the on-lock mechanism provided as such, the switch lever is held at the ON position without need of being held in the state after being pulled by the user, and the electric motor is locked in the state of activation. This accordingly increases the workability of the electric power tool, i.e., the ease of use of the switch device, so that the long-hour work can be performed with ease, for example. On the other hand, with the off-lock mechanism, after being once locked in the OFF position, the switch lever is not allowed to move to the ON position even if the user pulls the switch lever. This accordingly prevents the electric motor from being accidentally started.
For performing such a switching operation between the on-lock and off-lock mechanisms, DE3638952C2 proposes a lock operation member that utilizes the movement of the switch lever itself, and Japanese Laid-Open Patent Publication No. 9-290377 (Japanese Patent No. 2977076) proposed to use a lever, a push button, or others that are provided separately from the switch lever.
According to the known switch devices provided with both the on-lock and off-lock mechanisms, it is possible to improve the workability of the electric power tool and ease of use of the switch devices, and at the same time it is possible to prevent the electric power tool from being accidentally activated or to prevent the switch devices from being accidentally turned ON.
However, the known switch devices provided with both the on-lock and off-lock mechanisms are operated substantially in the same direction to release the off-lock mechanism and to activate the on-lock mechanism. Therefore, there has been a possibility that the user erroneously operates the switch devices to release the off-lock mechanism and to activate the on-lock mechanism as a series of operation.
Thus, when the user wants to use the electric power tool by releasing the switch lever from being in the off-lock state, i.e., in the state where the switch lever is not allowed to move to the ON position for operation due to the off-lock mechanism, he or she may accidentally activate the on-lock mechanism irrespective of his or her intention of operating the switch lever to only release it from being in the off-lock state, thereby locking the switch lever in the ON position. If this happens, even if the user stops pulling the switch lever to stop the electric power tool, the electric power tool remains in the state of activation. Hence, the known switch devices have the problem of the difficulty in specifically responding to the user's intension in terms of switching between the operation of releasing the switch lever from being in the off-lock state and the operation of putting the switch lever in the on-lock state.
Therefore, there is a need in the art for a switch device that includes both on-lock and off-lock mechanisms and can reliably respond to a user's intension in terms of switching between the operation of releasing the switch lever from being in the off-lock state and the operation of bringing the switch lever into the on-lock state.